After Update: all ratings are wrong

Hi,
after updating to the newest version the average rating is absolutely wrong. I use the comment form to let visitors rate for a product, but when I look at the comments, there is no voting less than 5 points, but the average rating shows f.e. 2,7 and so on…(https://www.fernstudium-bewertung.com/hochschulen/iubh). it seems that the ratings from all of my comments are confused and so the average rating is not representative enough.
where could be the mistake?

thank you

The page I need help with: [log in to see the link]